JP2014177371A - Titanium dioxide, lithium ion secondary battery, hybrid capacitor and method of producing titanium dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide titanium dioxide which is easy to synthesize and has excellent battery characteristics.SOLUTION: Titanium dioxide consists of a fine crystal aggregate as an aggregate of primary particles which are formed from titanium oxide containing an alkali metal. The primary particle has a laminar structure and is a spherical particle of a particle size of 1 μm or smaller, and the fine crystal aggregate has no orientation.

Description

  The present invention relates to a titanium dioxide serving as an electrode active material of a lithium ion secondary battery and a hybrid capacitor, a manufacturing method thereof, and a lithium ion secondary battery and a hybrid capacitor using titanium dioxide as an electrode active material.

  In power storage devices such as lithium ion secondary batteries and hybrid capacitors that are frequently used in recent years, charge and discharge are performed by movement of lithium ions in a solid phase and adsorption of positive and negative ions. These power storage devices are required to have higher energy density and higher output as the portable equipment used is smaller and higher in performance.

Currently, there are many positive electrode active materials for lithium ion secondary batteries, but the most commonly known one is lithium cobalt oxidation with an operating voltage of around 4 V (vs. Li / Li ⁺ ). It is a lithium-containing transition metal oxide having a basic structure of an oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide having a spinel structure (LiMn ₂ O ₄ ), or the like. These are widely employed as positive electrode active materials because of their excellent charge / discharge characteristics and energy density.
As the negative electrode active material, hard carbon, soft carbon, and a carbon material is widely used, such as graphite, which the LiPF ₆ in the electrolytic solution was dissolved in cyclic and linear carbonate are used.

  However, when considering the future development of medium-sized and large-sized batteries, especially for mounting on hybrid electric vehicles (HEVs) and electric vehicles (EVs), which are expected to be in great demand, The specifications cannot satisfy the safety and long life required for HEV and EV applications.

  Under such circumstances, studies have been made on using a titanium oxide-based active material as an electrode active material. This titanium oxide-based active material has a voltage of about 1-2 V when lithium metal is used for the counter electrode. Therefore, titanium oxide-based active materials having various crystal structures or particle shapes have been studied as electrode active materials.

Among them, titanium dioxide having a bronze type crystal structure (bronze type titanium oxide, hereinafter referred to as “TiO ₂ (B)”) is a spinel type represented by Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3). Its capacity is higher than that of lithium titanate, and has attracted attention as an electrode active material for lithium ion secondary batteries.

For example, a TiO ₂ (B) active material having a nanoscale shape such as a nanowire or a nanotube has attracted attention as an electrode material having an initial discharge capacity exceeding 300 mAh / g (see, for example, Non-Patent Document 1).

However, in these TiO ₂ (B) such as nanowires and nanotubes, a part of the lithium ions inserted by the initial insertion reaction is not desorbed, so the irreversible capacity increases due to the presence of lithium ions that are not released. As a result, the initial charge / discharge efficiency (= charge capacity (lithium desorption amount) ÷ discharge capacity (lithium insertion amount)) of TiO ₂ (B) such as nanowires and nanotubes is about 73%, and high capacity lithium ion 2 There was a problem in application as an electrode material in a secondary battery.

Moreover, the hydrothermal synthesis method unsuitable for mass production is used for the synthesis | combination of the alkali containing titanic acid used as these precursors. In addition, with these TiO ₂ (B) such as nanowires and nanotubes, the shape of the obtained particles is also anisotropic, making it difficult to produce a high-density electrode that is indispensable for maintaining a high energy density per volume. .

On the other hand, as a method for obtaining a precursor by a solid phase method suitable for mass production, a method via Na ₂ Ti ₃ O ₇ or K ₂ Ti ₄ O ₉ which is a precursor by high-temperature firing is disclosed. (For example, refer to Patent Document 1, Patent Document 2, and Patent Document 3).

JP 2011-241100 A JP 2008-34368 A JP 2008-117625 A

A. R. Armstrong, G. Armstrong, J. Canales, R. Garcia, P. G. Bruce, Advanced Materials, 17, 862-865 (2005)

  However, according to these Patent Document 1, Patent Document 2 and Patent Document 3, it is necessary to repeat high-temperature calcination twice for the synthesis of a pure precursor, and the proton exchange reaction also involves replacing the hydrochloric acid solution every 12 hours. In addition, it is complicated that it is necessary to continue the processing for 5 days.

Further, TiO ₂ (B) disclosed in Patent Document 1 has an initial discharge capacity as high as 200 mAh / g, but it has been clarified that the capacity decrease at a high current density is remarkably large. Further, it has been clarified that TiO ₂ (B) disclosed in Patent Document 2 cannot obtain a sufficient initial discharge capacity and initial charge / discharge efficiency. Further, TiO ₂ (B) disclosed in Patent Document 3 can greatly improve the electrochemical characteristics, but the difficulty in synthesis is unsolved.

  The present invention has been made in order to solve the above-described problems. Titanium dioxide, which is easy to synthesize and has excellent battery characteristics, a lithium ion secondary battery and a hybrid capacitor using titanium dioxide as a negative electrode active material, and An object of the present invention is to provide a method for producing titanium dioxide.

  In the titanium dioxide according to the present invention, titanium dioxide is a microcrystalline aggregate as an aggregate of primary particles generated from titanium oxide containing an alkali metal, and the primary particles have a layered structure, It is a spherical particle having a particle diameter of 1 μm or less, and the microcrystalline aggregate has no orientation.

  The disclosed titanium dioxide can provide a lithium ion secondary battery exhibiting excellent initial discharge capacity and initial charge / discharge efficiency when used as an electrode material of a lithium ion secondary battery, and as a negative electrode of a hybrid capacitor. Also has the effect that can be used.

(A) is an SEM image of a precursor (K ₂ Li _0.6 Ti ₄ O _9.3 ) obtained by firing at 700 ° C., and (b) is a precursor (K) obtained by firing at 800 ° C. ₂ Li _0.6 Ti ₄ O _9.3 ), and (c) is an SEM image of a precursor (K ₂ Li _0.6 Ti ₄ O _9.3 ) obtained by firing at 900 ° C. And (d) is an SEM image of a precursor (K ₂ Li _0.6 Ti ₄ O _9.3 ) obtained by firing at 1000 ° C. It is an X-ray diffraction (XRD) figure of the 350 degreeC heat processing sample after 3N nitrate proton exchange reaction. (A) is a graph which shows the dQ / dV curve of the lithium battery which used the titanium dioxide sample synthesize | combined from the precursor which makes baking temperature 700 degreeC as an active material, and used metallic lithium for the negative electrode, (b) is an Example. 1 is a characteristic diagram showing discharge rate characteristics and cycle characteristics of Example 1 and Example 2. FIG.

(First embodiment of the present invention)
Titanium dioxide (TiO ₂ ) according to this embodiment is a microcrystalline aggregate as an aggregate of primary particles generated from a titanium oxide containing an alkali metal, and has no orientation.
The primary particles of titanium dioxide are spherical particles having a layered structure and a particle diameter of 1 μm or less.

Moreover, the titanium oxide according to the present embodiment contains two types of lithium (Li) and potassium (K), rubidium (Rb) or cesium (Cs), or one type of cesium (Cs) as an alkali metal. And it becomes a precursor of titanium dioxide having a layered structure with a predetermined composition.
In particular, the titanium oxide according to the present embodiment includes K _x Li _y Ti _{2− (x + y) / 4} O ₄ (where 3 <(x / y) <3.6), Rb _x Li _y Ti _{2− ( x + y) / 4} O ₄ (where 3 <(x / y) <3.5), Cs _x Li _y Ti _{2− (x + y) / 4} O ₄ where 3 <(x / y) <3.5 ) Or Cs _x Ti _{2-x / 4} O ₄ (where 0.7 <x <0.9).

  In addition, the method for producing titanium dioxide according to the present embodiment includes a firing step of firing an alkali metal-containing titanium oxide at 500 ° C. to 800 ° C., and impregnating the fired titanium oxide in an acidic aqueous solution to titanate. And at least a titanium dioxide production step of producing titanium dioxide by firing the produced titanic acid.

  The present inventor has shown that the use of a precursor (titanium oxide) having a lepidocrocite structure having a layered structure is effective in producing titanium dioxide that is easy to synthesize and has excellent battery characteristics. And found as follows.

A precursor having a repidocrocite structure having a layered structure can be synthesized in a wide temperature range (500 ° C. to 1000 ° C.).
In particular, as shown in FIGS. 1 (a) and 1 (b), the precursor obtained by low-temperature firing at 800 ° C. or less has a primary particle size (primary particle size) of 1 μm or less (700 ° C .: about 0). 0.5 μm, 800 ° C .: about 1 μm), but the precursor synthesized by high-temperature firing at 900 ° C. or higher is composed of primary particles as shown in FIG. 1 (c) and FIG. 1 (d). Crystals having a particle size of several tens of microns (900 ° C .: 5 μm to 10 μm, 1000 ° C .: 30 μm to 80 μm) are given.

  Also, the primary particle crystals grow as the precursor firing temperature increases and grow into tabular crystals (700 ° C .: spherical particles, 800 ° C .: somewhat tabular particles, 900 ° C .: tabular particles, 1000 ° C. : Tabular grains). Further, the precursor synthesized by high-temperature firing is evaluated by X-ray diffraction (XRD), and the diffraction of the (0k0) plane at 12 ° and 28 °, which are 2θ values measured using CuKα rays. The intensity ratio of the line changes. The ratio of the intensity of the (020) plane diffraction line to the intensity of the (130) plane diffraction line ((020) / (130) intensity ratio) is 0.85 at a firing temperature of 700 ° C., and the firing temperature of 800 0.84 at ℃, 1.74 at a calcination temperature of 900 ° C, 2.39 at a calcination temperature of 1000 ° C, and the grains grow and align in a plate shape by high-temperature calcination at 900 ° C or higher. The intensity of the 020) plane diffraction line is increased.

  Moreover, the precursor synthesized by high-temperature firing is easily cleaved along the (020) plane by applying a proton exchange reaction, and the thickness in the b-axis direction is remarkably reduced. The titanic acid produced | generated here transfers to the titanium dioxide of a bronze phase by heat processing at 250 degreeC or more by heat processing.

It should be noted that the diffusion of lithium ions (Li ⁺ ) in the solid is an important factor in the performance of the lithium ion secondary battery. In order to maintain the high performance of the lithium ion secondary battery when the diffusion rate of lithium ions in the solid is slow, it is necessary to reduce the diffusion distance by making fine particles of titanium dioxide. Further, when used as a battery material of a lithium ion secondary battery, lithium ions diffuse in the tunnel in the c-axis direction of the bronze phase. This direction is the c-axis direction of titanic acid, that is, a direction parallel to the cleavage plane, and the length in the diffusion direction is not reduced even if the crystal is reduced by cleavage. For this reason, the precursor synthesized by high-temperature firing does not lead to improvement of battery characteristics even if the cleavage is advanced to make fine particles.

As precursors used for the synthesis of titanium dioxide, Na ₂ Ti ₃ O ₇ , K ₂ Ti ₄ O _9, Cs ₂ Ti ₅ O _11, etc. whose interface is stepped and whose layer is a layered structure are known. In order to synthesize them in a single phase, high-temperature firing is indispensable.
As a result, the synthetic sample forms primary particles of 1 μm or more having a rod-like shape reflecting the crystal form. In the ion exchange process, the shape is maintained, and in the subsequent heat treatment, titanium dioxide having a long lithium ion diffusion distance is generated, resulting in poor battery characteristics.

  From this point of view, the lipidocrosite phase becomes a microcrystalline aggregate by baking and synthesizing titanium oxide at a low temperature of 500 ° C. to 800 ° C., and is optimal as a precursor of titanium dioxide.

Moreover, the proton exchange reaction of the lipidocrosite phase is complicated. For example, when K _0.86 Ti _1.72 Li _0.26 O ₄ synthesized at 900 ° C. is subjected to proton exchange at 3 mol / L hydrochloric acid (3N HCl) while changing the temperature, all the reactions are completed within 24 hours. However, when the proton exchange temperature is 80 ° C. or higher, a rutile phase and an anatase phase are by-produced, and the higher the proton exchange temperature, the more preferential production of these phases is. For this reason, it is necessary to perform proton exchange temperature at 70 degrees C or less. The position of the titanic acid diffraction peak appearing on the low angle side also depends on the temperature, and appears on the low angle side most near room temperature. In this case, a feature is that many (0k0) plane diffraction lines appear strongly.

The particle size of the precursor greatly depends on the yield of titanic acid. For example, when hydrochloric acid is used for the proton exchange reaction and potassium ions (K ⁺ ) and lithium ions (Li ⁺ ) are ion-exchanged to protons, the amount is 70% or more on a weight basis in the case of 3 mol / L (3N) or less. Titanic acid can be recovered. When the acid concentration is increased to 5 mol / L hydrochloric acid (5N HCl), the yield of titanic acid is reduced to 10% or less in the precursor synthesized at a firing temperature of 600 to 800 ° C. with a small primary particle size.

  In addition, hydrochloric acid and nitric acid can be used for the synthesis of titanic acid from the precursor, but hydrochloric acid can be completely removed in the heat treatment process, and the first cycle of the bronze phase to be synthesized finally. Since the irreversible capacity is reduced and the irreversible capacity can be suppressed to a minimum, hydrochloric acid is preferable in producing battery materials.

Further, the sample after the proton exchange reaction (intermediate titanic acid) has an interlayer distance d of 9.22 mm when the precursor firing temperature is 700 ° C., and an interlayer when the precursor firing temperature is 800 ° C. When the distance d is 9.22 mm, when the precursor baking temperature is 900 ° C., the interlayer distance d is 8.20 mm, and when the precursor baking temperature is 1000 ° C., the interlayer distance d is 7.53 mm. Therefore, the higher the temperature of the precursor, the shorter the interlayer distance.
For this reason, the sample after the proton exchange reaction to the precursor calcined at high temperature (intermediate titanic acid) is one in which moisture does not co-insert when the crystallinity of the precursor is good. The removal amount is small and the weight loss is small.

  In addition, titanic acid can be synthesized from various precursors, but the X-ray diffraction (XRD) diagram, infrared absorption spectrum, and Raman spectrum of titanic acid synthesized from each precursor are similar, and the difference is clarified. It is difficult to do. However, the temperature range of formation of the bronze phase that occurs in the intermediate process of the transition to the anatase phase during the heat treatment process of titanic acid depends on the crystallinity and composition of the precursor.

  For example, in the case of a K—Li-based lipidocrosite phase synthesized at 900 ° C., the heat treatment temperature at which the X-ray diffraction (XRD) diffraction line derived from titanic acid disappears is about 250 ° C. regardless of the composition of the precursor. However, the transition to the anatase phase hardly occurs when the K / Ti atomic ratio of the precursor is 0.5, and the presence of the anatase phase is not detected by electrochemical measurement even at 450 ° C. That is, in order to synthesize a bronze phase with good reproducibility, it is desirable to set the K / Li atomic ratio of the precursor to 0.5.

  The firing temperature of the precursor is also related to the transition temperature to the anatase phase. For example, titanic acid obtained from a precursor synthesized at 900 ° C. did not show transition to the anatase phase by heat treatment at 450 ° C., but titanic acid obtained from a precursor synthesized at 1000 ° C. It was confirmed that a part of the anatase phase was transferred by heat treatment at ℃. That is, it has been clarified that titanic acid obtained from a precursor with poor crystallinity at low temperature firing is less likely to transition to the anatase phase.

Note that the difference in the X-ray diffraction (XRD) diagram between titanium dioxide obtained from a precursor for high-temperature firing and titanium dioxide obtained from a precursor for low-temperature firing is not so great. However, as shown in FIG. 2, peak splitting and peak intensity increase around 15 ° or 30 °, which is the value of 2θ measured using CuKα rays, continue as the precursor firing temperature increases. Will occur. That is, the firing temperature of the precursor has an influence on the crystallinity of titanium dioxide. The high temperature firing precursor of 900 ° C. or higher has high crystallinity, and the low temperature firing precursor of 800 ° C. or lower has low crystallinity. have. The X-ray diffraction (XRD) diagram shown in FIG. 2 shows protons using ₃ mol / L nitric acid (3N HNO ₃ ) when the firing temperature of the precursor is 700 ° C., 800 ° C., 900 ° C., and 1000 ° C. It is the result of performing X-ray diffraction (XRD) with respect to the sample which obtained titanic acid by the exchange reaction and heat-processed this titanic acid at 350 degreeC. Further, the X-ray diffraction (XRD) diagram surrounded by a two-dot chain line shown in FIG. 2 is a result of performing X-ray diffraction (XRD) on the sample according to the present embodiment.

The characteristics of titanium dioxide synthesized from the low-temperature firing precursor according to the present embodiment appear in the Raman spectrum and the charge / discharge behavior except for the particle form.
Among these, regarding the shape of the Raman spectrum, the spectrum shape of titanium dioxide (low crystalline TiO ₂ ) according to this embodiment is the conventional titanium dioxide (high crystalline TiO ₂ (B): precursor firing temperature of 900 ° C. or more. , Raman shift [cm ⁻¹ ]: 295, 360, 430, 470, 550) rather than the spectral shape of titanic acid. That is, the Raman spectrum of the titanium dioxide according to the present embodiment (low crystalline TiO ₂₎ is the peak near 510 cm ^-1 is not present in the titanate is present, peak in 548cm ^-1 is not observed, 367cm ^-1 This peak has only an intensity that is a shoulder peak of a peak at 410 cm ⁻¹ .
Considering this result together with the measurement result by X-ray diffraction (XRD), it can be determined that the titanium dioxide according to the present embodiment is an intermediate structure between the layered structure and the bronze phase.

In addition, when a charge / discharge test was performed using the titanium dioxide according to the present embodiment as an active material and the counter electrode as metallic lithium, titanium dioxide produced from a precursor having a firing temperature of 700 ° C. and 800 ° C. is also a bronze phase TiO 2. It gave charge-discharge curve similar to the _second charge-discharge curve. Further, as shown in Table 1 below, it can be seen that titanium dioxide synthesized from 700 ° C. and 800 ° C. precursors has a large reversible capacity.

Further, the feature of the titanium dioxide according to the present embodiment is that it has an excellent discharge rate characteristic when used as an active material of a lithium secondary battery as compared with conventional titanium dioxide (TiO ₂ (B)). It is. For example, in titanium dioxide where the firing temperature of the precursor is 700 ° C., only a decrease in capacity of 10% or less is observed from 0.05 C to 0.8 C, and a capacity of 180 mAh / g or more is maintained even at 1.6 C. I understand that. Note that 1C in the present embodiment is calculated with a nominal capacity value of 220 mAhg- ¹ .

Moreover, when the titanium dioxide which concerns on this embodiment is used for the active material of a lithium secondary battery, it will appear when a charge / discharge rate is lowered to about 0.05C as a feature of a charge / discharge curve. Further, the titanium dioxide according to the present embodiment is composed of two plateaus in a region where the charge / discharge curve, particularly the charge curve is 1.8 V or less. This can be clarified by differentiating the charge / discharge curve. This differential value (dQ / dV: Q is a capacity, V is a voltage), while high crystalline titanium dioxide (TiO ₂ (B)) has only one peak on the high voltage side, FIG. ), The titanium dioxide according to the present embodiment (Example 1) gives another peak on the low voltage side of the highly crystalline TiO ₂ (B).

  Next, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

Example 1
First, 7.99 g of anatase-type titanium dioxide, 3.46 g of potassium carbonate, and 1.53 g of lithium acetate, which are raw materials, were placed in a mortar and mixed with a small amount of water.
The mixed raw material was transferred to an evaporating dish, dehydrated at 200 ° C., and dried.
Furthermore, this dried mixture was baked at 500 ° C., 600 ° C. or 700 ° C. for 20 hours to produce K ₂ Li _0.6 Ti ₄ O _9.3 which is a precursor of titanium dioxide.

  A product calcined at 500 ° C. (a sample calcined at 500 ° C.), a product calcined at 600 ° C. (a calcined sample at 600 ° C.), and a product calcined at 700 ° C. (a calcined sample at 700 ° C.) by an X-ray diffraction (XRD) method. As a result of analysis, all the products were single-phase lepidocrotite phases not containing the raw material anatase phase.

  Moreover, as a result of observing these precursors (500 ° C. calcined sample, 600 ° C. calcined sample, 700 ° C. calcined sample) with a scanning electron microscope (SEM), the particle size of primary particles in all the precursors Was composed of spherical fine particles of 1 μm or less (see FIG. 1A).

Next, 2 g of a 700 ° C. calcined sample was taken and immersed in 100 ml of 3 mol / L hydrochloric acid (3N HCl) at 0 ° C. to 70 ° C. (preferably normal temperature) overnight (12 hours). And the supernatant liquid was removed and 50 ml of distilled water was added.
These operations were repeated 5 times, followed by filtration and drying at 80 ° C. for one day to obtain titanic acid.

  When the obtained titanic acid was evaluated by X-ray diffraction (XRD), the diffraction line of the precursor did not remain and it was confirmed that the precursor was completely changed to titanic acid.

  This titanic acid sample was heat treated in air at 150 ° C., 250 ° C., 350 ° C. or 450 ° C. for 4 hours to obtain titanium dioxide.

When these titanium dioxides were analyzed by the X-ray diffraction (XRD) method, the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 250 ° C. or lower showed that 2θ measured using CuKα rays was 12 °. And at 24 °, a sharp peak derived from titanic acid remains.
In addition, in the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 350 ° C., there is no sharp peak, and there is only a broad peak corresponding to the bronze phase.
Similarly, an X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 450 ° C. is a diffraction diagram in which a broad peak corresponding to the bronze phase exists, but the 2θ measured using CuKα rays. The peak intensities near the values of 15 ° and 30 ° increased, and the diffraction pattern was more bronze phase.
Titanium dioxide obtained by heat-treating titanic acid at 350 ° C. or 450 ° C. has a smaller number of peaks, wider X-ray diffraction image line width, and strength than conventional titanium dioxide (TiO ₂ (B)). It is a weak amorphous material and has no characteristics of titanic acid.

Moreover, when the Raman spectrum in these titanium dioxide samples was measured, the samples obtained by heat-treating titanic acid at 150 ° C., 250 ° C. and 350 ° C. are generally similar.
However, as a major difference, in the X-ray diffraction (XRD), the sample heat-treated at 350 ° C. belonging to bronze phase titanium dioxide has a peak in the vicinity of 510 cm ⁻¹ which does not exist in titanic acid.
Further, when the heat treatment temperature is raised from 350 ° C. to 450 ° C., the Raman spectrum also changes to a spectrum peculiar to bronze phase titanium dioxide.

Next, an electrode was prepared using titanium dioxide obtained by heat-treating titanic acid at 350 ° C. as an active material. For the preparation of the electrode, 12 mg of a conductive binder composed of acetylene black and Teflon (registered trademark) was used, and the active material was 20 mg.
Further, the electrolyte, 1M LiPF ₆ (lithium hexafluorophosphate) / ethylene carbonate (ethylene carbonate: EC) - dimethyl carbonate (Dimethyl carbonate: DMC) was used.
And the electrode which used the titanium dioxide which concerns on a present Example for an active material, and a metal lithium counter electrode are combined, and a lithium secondary battery is comprised with electrolyte solution.
The titanium dioxide according to this embodiment used for the negative electrode corresponds to the bronze phase in terms of X-ray diffraction (XRD), and has a layered structure in terms of Raman spectrum.

The charge and discharge of the lithium secondary battery provided with these electrodes and electrolyte solution is performed at room temperature, and the discharge rate characteristics and cycle characteristics with a current density of 0.1 mA / cm ² (0.05 C) or more are shown in FIG. Shown in b).
As shown in FIG. 3 (b), the discharge rate characteristics and cycle characteristics maintained a capacity of 80% or more even when the discharge rate was increased from 0.05C to 1.6C. Even if it returns, discharge capacity is maintaining the same value as the beginning, and cycling characteristics are also favorable.

Further, the charge-discharge curves of the electrode and a lithium secondary battery electrolyte having a (Example 1), a lithium secondary were produced from the precursor synthesized at a high temperature highly crystalline TiO 2 _(B) and the active material It has a shape that is not found in the battery (Comparative Example 1). That is, as shown in the differential curve (dQ / dV) of FIG. 3A, the lithium secondary battery according to Example 1 has a new peak on the low voltage side as compared with the lithium secondary battery according to Comparative Example 1. It is a feature to have.

  In addition, charging / discharging of the lithium secondary battery provided with the above electrode and electrolyte solution confirms that the charging / discharging voltage range is from 1.2 V to 2.5 V and a capacity of 180 mAh / g per 1 g of titanium dioxide is obtained. We were able to.

(Example 2)
First, 10.0 g of anatase-type titanium dioxide, 6.20 g of rubidium carbonate, and 0.66 g of lithium carbonate, which are raw materials, were placed in a mortar and mixed with a small amount of water.
The mixed raw material was transferred to an evaporating dish, dehydrated at 350 ° C., and dried.
Furthermore, this dried mixture was baked at 600 ° C. or 700 ° C. for 20 hours to produce Rb _0.75 Li _0.25 Ti _1.75 O ₄ which is a precursor of titanium dioxide.

  As a result of analyzing the product calcined at 600 ° C. (600 ° C. calcined sample) and the product calcined at 700 ° C. (700 ° C. calcined sample) by the X-ray diffraction (XRD) method, both products showed the raw anatase phase. It was a single-phase lepidocrotite phase not contained.

  Moreover, as a result of observing these precursors (600 ° C. calcined sample, 700 ° C. calcined sample) with a scanning electron microscope (SEM), all the precursors are composed of spherical fine particles having a primary particle size of 1 μm or less. I found out that

Next, 2 g of a 700 ° C. calcined sample was taken and immersed in 100 ml of 3 mol / L hydrochloric acid (3N HCl) at 0 ° C. to 70 ° C. (preferably normal temperature) overnight (12 hours). And the supernatant liquid was removed and 50 ml of distilled water was added.
These operations were repeated 5 times, followed by filtration and drying at 80 ° C. for one day. And this operation was repeated twice or three times to obtain titanic acid.

  When the obtained titanic acid was evaluated by X-ray diffraction (XRD), the diffraction line of the precursor did not remain, and it was confirmed that the precursor was completely changed to titanic acid.

  This titanic acid sample was heat treated in air at 250 ° C., 350 ° C., 500 ° C. or 700 ° C. for 4 hours to obtain titanium dioxide.

When these titanium dioxides were analyzed by the X-ray diffraction (XRD) method, the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 250 ° C. or lower showed that 2θ measured using CuKα rays was 12 °. And at 24 °, a sharp peak derived from titanic acid remains.
In addition, in the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 350 ° C., there is no sharp peak, and there is only a broad peak corresponding to the bronze phase.
Similarly, an X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 500 ° C. is a diffraction diagram in which a broad peak corresponding to the bronze phase exists, but the 2θ measured using CuKα rays. The peak intensities near the values of 15 ° and 30 ° increased, and the diffraction pattern was more bronze phase.
Furthermore, the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 700 ° C. was a diffractogram converted to an anatase phase.
The purity of titanic acid can also be confirmed by X-ray diffraction (XRD) measurement of a heat-treated product of titanic acid. In addition, in the case of titanic acid containing an alkali metal obtained by repeating the proton exchange reaction twice, an X-ray diffraction (XRD) diagram of titanium dioxide heat-treated at 800 ° C. shows a trace amount in addition to the anatase phase of the main product. Of lepidocrotite phase was observed. That is, the alkali metal cannot be completely removed by two ion exchanges. However, if the proton exchange reaction is repeated three times, the presence of the lipidocrosite phase cannot be confirmed in X-ray diffraction (XRD) measurement, and trace amounts of alkali metals can be removed by three ion exchange treatments. It will be possible.

Next, an electrode was prepared using titanium dioxide obtained by heat-treating titanic acid obtained by performing ion exchange reaction with 3 mol / L hydrochloric acid (3N HCl) three times at 500 ° C. as an active material. For the production of the electrode, 12 mg of a conductive binder composed of acetylene black and Teflon (registered trademark) was used, and the negative electrode active material was 20 mg.
Further, the electrolyte, 1M LiPF ₆ (lithium hexafluorophosphate) / ethylene carbonate (EC) - was used dimethyl carbonate (DMC).
And the electrode which used the titanium dioxide which concerns on a present Example for an active material, and a metal lithium counter electrode are combined, and a lithium secondary battery is comprised with electrolyte solution.

Then, in order to reduce the polarization, the measurement temperature was set to 50 ° C., the lithium secondary battery including these electrodes and the electrolyte was charged and discharged, the current density was set to 0.4 mA / cm ² , and the battery characteristics were evaluated. . When the obtained charge / discharge curve was differentiated and the differential curve (dQ / dV) was calculated, the presence of two charge / discharge plateaus could be confirmed.

(Example 3)
First, 10.0 g of anatase-type titanium dioxide, 8.07 g of cesium carbonate, and 0.60 g of lithium carbonate, which are raw materials, were placed in a mortar and mixed with a small amount of water.
The mixed raw material was transferred to an evaporating dish, dehydrated at 350 ° C., and dried.
Furthermore, this dried mixture was baked at 600 ° C. or 700 ° C. for 20 hours to produce Cs _0.7 Li _0.23 Ti _1.77 O ₄ which is a precursor of titanium dioxide.

  As a result of analyzing the product calcined at 600 ° C. (600 ° C. calcined sample) and the product calcined at 700 ° C. (700 ° C. calcined sample) by the X-ray diffraction (XRD) method, both products showed the raw anatase phase. It was a single-phase lepidocrotite phase not contained.

  Moreover, as a result of observing these precursors (600 ° C. calcined sample, 700 ° C. calcined sample) with a scanning electron microscope (SEM), all the precursors are composed of spherical fine particles having a primary particle size of 1 μm or less. I found out that

Next, 2 g of a 700 ° C. calcined sample was taken and immersed in 100 ml of 3 mol / L hydrochloric acid (3N HCl) at 0 ° C. to 70 ° C. (preferably normal temperature) overnight (12 hours). And the supernatant liquid was removed and 50 ml of distilled water was added.
These operations were repeated 5 times, followed by filtration and drying at 80 ° C. for one day. And this operation was repeated 5 times to obtain titanic acid.

  When the obtained titanic acid was evaluated by X-ray diffraction (XRD), the diffraction line of the precursor did not remain, and it was confirmed that the precursor was completely changed to titanic acid.

  This titanic acid sample was heat treated in air at 250 ° C., 350 ° C., 500 ° C. or 700 ° C. for 4 hours to obtain titanium dioxide.

When these titanium dioxides were analyzed by the X-ray diffraction (XRD) method, the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 250 ° C. or lower showed that 2θ measured using CuKα rays was 12 °. And at 24 °, a sharp peak derived from titanic acid remains.
In addition, in the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 350 ° C., there is no sharp peak, and there is only a broad peak corresponding to the bronze phase.
Similarly, an X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 500 ° C. is a diffraction diagram in which a broad peak corresponding to the bronze phase exists, but the 2θ measured using CuKα rays. The peak intensities near the values of 15 ° and 30 ° increased, and the diffraction pattern was more bronze phase.
Furthermore, in the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 700 ° C., the anatase phase is the main component, but contamination of the impurity phase is observed. That is, the alkali metal cannot be completely removed by one ion exchange. However, when the proton exchange reaction is repeated three times, the alkali metal can be removed, and the presence of a lipidocrosite phase is confirmed in X-ray diffraction (XRD) measurement even at 700 ° C. Will not be able to.
Therefore, it was clarified that the removal of the alkali metal depends on the constituent elements of the precursor and is difficult to remove in the order of potassium, rubidium, and cesium.

Next, an electrode was prepared using titanium dioxide obtained by heat-treating titanic acid obtained by performing ion exchange reaction with 3 mol / L hydrochloric acid (3N HCl) five times at 500 ° C. as an active material. For the production of the electrode, 12 mg of a conductive binder composed of acetylene black and Teflon (registered trademark) was used, and the electrode active material was 20 mg.
Further, the electrolyte, 1M LiPF ₆ (lithium hexafluorophosphate) / ethylene carbonate (EC) - was used dimethyl carbonate (DMC).
And the electrode using the titanium dioxide which concerns on a present Example and the metal lithium counter electrode are combined, and a lithium secondary battery is comprised with electrolyte solution.

In order to suppress polarization, the measurement temperature was set to 50 ° C., and the lithium secondary battery provided with this electrode and the electrolyte was charged and discharged, and the battery characteristics were evaluated. The current density was 0.4 mA / cm ² . When the obtained charge / discharge curve was differentiated and the differential curve (dQ / dV) was calculated, the presence of two charge / discharge plateaus could be confirmed.

Example 4
First, 10.0 g of anatase-type titanium dioxide and 8.07 g of cesium carbonate as raw materials were placed in a mortar and mixed with a small amount of water.
The mixed raw material was transferred to an evaporating dish, dehydrated at 200 ° C., and dried.
Furthermore, this dried mixture was baked at 600 ° C. or 700 ° C. for 20 hours to produce Cs _0.73 Ti _1.82 O ₄ which is a precursor of titanium dioxide.

  The product calcined at 600 ° C. (600 ° C. calcined sample) and the product calcined at 700 ° C. (700 ° C. calcined sample) were analyzed by the X-ray diffraction (XRD) method. As a result, 2θ = 28 measured using CuKα rays. Although the peak at 0 ° was broad, all the products were single-phase lepidocrotite phases that did not contain the starting anatase phase.

  Moreover, as a result of observing these precursors (600 ° C. calcined sample, 700 ° C. calcined sample) with a scanning electron microscope (SEM), all the precursors are composed of spherical fine particles having a primary particle size of 1 μm or less. I found out that

Next, 2 g of a 700 ° C. calcined sample was taken and immersed in 100 ml of 3 mol / L hydrochloric acid (3N HCl) at 0 ° C. to 70 ° C. (preferably normal temperature) overnight (12 hours). And after filtering a 700 degreeC baking sample, 100 ml of 3 mol / L hydrochloric acid (3N HCl) was added again, and it was immersed overnight (12 hours). These operations were performed 5 times in total. And the supernatant liquid was removed and 50 ml of distilled water was added.
These operations were repeated 5 times, followed by filtration and drying at 80 ° C. for one day to obtain titanic acid.

  This titanic acid sample was heat treated in air at 500 ° C. or 800 ° C. for 4 hours to obtain titanium dioxide.

  When these titanium dioxides were analyzed by the X-ray diffraction (XRD) method, only a broad peak corresponding to the bronze phase exists in the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat-treating titanic acid at 500 ° C. . On the other hand, in the X-ray diffraction (XRD) diagram of titanium dioxide obtained by heat treating titanic acid at 800 ° C., it was confirmed that this titanium dioxide was a single phase of anatase phase.

Next, an electrode was prepared using this titanium dioxide as an active material. For the preparation of the electrode, 12 mg of a conductive binder composed of acetylene black and Teflon (registered trademark) was used, and the active material was 20 mg.
Further, the electrolyte, 1M LiPF ₆ (lithium hexafluorophosphate) / ethylene carbonate (EC) - was used dimethyl carbonate (DMC).
The electrode using the titanium dioxide according to the present embodiment as an active material and a metal lithium counter electrode are combined to form a lithium secondary battery together with the electrolytic solution.

Then, in order to suppress polarization, the measurement temperature was set to 50 ° C., and the lithium secondary battery including the electrode and the electrolytic solution was charged and discharged, the current density was set to 0.4 mA / cm ² , and the battery characteristics were evaluated. When the obtained charge / discharge curve was differentiated and the differential curve (dQ / dV) was calculated, the presence of two charge / discharge plateaus could be confirmed.

(Example 5)
Bronze-phase titanium oxide according to the present invention synthesized in Example 1, lithium cobaltate (LiCoO ₂ ) of 4V class positive electrode material or LiNi _0.5 Mn _1.5 O ₂ of spinel structure of 5V class positive electrode material, Were combined to form a lithium ion secondary battery. In addition, the electrode preparation method and electrolyte solution are the same as that of the case of the above-mentioned lithium secondary battery.

When lithium cobaltate (LiCoO ₂ ) was used as the positive electrode, titanium oxide was used at 10.4 mg per 13.5 mg of lithium cobaltate. The measurement temperature was 50 ° C., the current density was 40 mA / g (per weight of the negative electrode), and the charge / discharge voltage was 1.0 V to 3.15 V.
Charging / discharging occurs at 2 V or higher, and the voltage continuously changes linearly. The Coulomb efficiency at the first cycle was 80%, and the capacity per negative electrode weight was 200 mAh / g. Further, there was no significant change in the discharge curve at the second cycle, and the discharge capacity was maintained.

In the case of using LiNi _0.5 Mn _1.5 O ₂ having a spinel structure as a positive electrode, titanium oxide was used at 10.2 mg with respect to 13.3 mg of LiNi _0.5 Mn _1.5 O ₂ . The measurement temperature was 50 ° C., and the current density was 40 mA / g (per negative electrode weight). Since the charge / discharge voltage has a high positive electrode voltage, the upper limit voltage was 3.6 V, and the voltage was 1.0 V to 3.6 V.
The charge in the first cycle consists of a plateau based on oxygen deficiency of the spinel positive electrode near 2V and a plateau near 3V. The discharge capacity at the first cycle was 140 mAh / g, but the second cycle was greatly degraded at 115 mAh / g. This is due to the positive electrode material, and is caused by oxygen deficiency and manganese dissolution.
Thus, the bronze phase titanium oxide according to the present invention can produce a lithium battery in combination with a 4V class positive electrode material or a 5V class positive electrode material.

(Comparative Example 1)
First, 7.99 g of anatase-type titanium dioxide, 3.46 g of potassium carbonate, and 1.53 g of lithium acetate, which are raw materials, were placed in a mortar and mixed with a small amount of water.
The mixed raw material was transferred to an evaporating dish, dehydrated at 200 ° C., and dried.
Furthermore, this dried mixture was baked at 900 ° C. or 1000 ° C. for 20 hours to produce K ₂ Li _0.6 Ti ₄ O _9.3 which is a precursor of titanium dioxide.

  As a result of analyzing the product calcined at 900 ° C. (900 ° C. calcined sample) and the product calcined at 1000 ° C. (1000 ° C. calcined sample) by the X-ray diffraction (XRD) method, both products showed the raw anatase phase. It was a single-phase lepidocrotite phase not contained (see FIG. 2).

  Moreover, as a result of observing these precursors (900 degreeC baking sample, 1000 degreeC baking sample) with a scanning electron microscope (SEM), in all the precursors, the particle diameter of a primary particle is a comparison with an angle | corner of 3 micrometers-10 micrometers. It was found that it was composed of objective tabular grains (see FIGS. 1C and 1D).

Next, 2 g of these precursors (900 ° C. calcined sample, 1000 ° C. calcined sample) are taken, and overnight (12 hours) in 100 ml of 3 mol / L hydrochloric acid (3N HCl) at 0 ° C. to 70 ° C. (preferably normal temperature). Soaked. And the supernatant liquid was removed and 50 ml of distilled water was added.
These operations were repeated 5 times, followed by filtration and drying at 80 ° C. for one day to obtain titanic acid.

  When the obtained titanic acid was evaluated by X-ray diffraction (XRD), the diffraction line of the precursor did not remain, and it was confirmed that the precursor was completely changed to titanic acid.

  Moreover, when the obtained titanic acid was observed with a scanning electron microscope (SEM), it was cleaved along the (020) plane, and the shape of the primary particles was a flat plate having a thickness of 0.1 μm to 0.2 μm. I found it changing. That is, it can be seen that the cleavage phenomenon is more likely to proceed with titanic acid using a precursor baked at high temperature than titanic acid using a precursor baked at high temperature.

  A titanic acid sample obtained from a 900 ° C. calcined sample (precursor) was heat treated in air at 450 ° C. for 4 hours to obtain titanium dioxide.

  When this titanium dioxide was analyzed by the X-ray diffraction (XRD) method, this sample became a typical bronze phase diffraction diagram, and peaks around 15 ° and 30 °, which were 2θ values measured using CuKα rays. I found that it was split into two.

Further, when the Raman spectrum of the titanium dioxide sample was measured, it was a spectrum of a typical bronze phase having peaks at 548 cm ⁻¹ and 367 cm ⁻¹ .

Next, an electrode was prepared using titanium dioxide obtained by heat-treating titanic acid at 450 ° C. as an active material. For the preparation of the electrode, 12 mg of a conductive binder composed of acetylene black and Teflon (registered trademark) was used, and the active material was 20 mg.
Further, the electrolyte, 1M LiPF ₆ (lithium hexafluorophosphate) / ethylene carbonate (EC) - was used dimethyl carbonate (DMC).
And the electrode which used the titanium dioxide which concerns on this comparative example 1 for an active material, and a metal lithium counter electrode are combined, and a lithium secondary battery is comprised with electrolyte solution.

  The charge / discharge curve of the lithium secondary battery (Comparative Example 1) provided with the electrode and the electrolytic solution had only one peak at 2 V or less.

(Comparative Example 2)
First, 7.9 g of anatase-type titanium dioxide and 5.8 g of cesium hydroxide as raw materials were placed in a mortar and mixed with a small amount of water.
The mixed raw material was transferred to an evaporating dish, dehydrated at 200 ° C., and dried.
Furthermore, this dried mixture was baked at 900 ° C. for 20 hours to produce Cs _0.73 Ti _1.82 O ₄ which is a precursor of titanium dioxide.

As a result of observing this precursor (900 ° C. calcined sample) with a scanning electron microscope (SEM), the surface was smooth and had a rod-like particle form with a short axis of 0.5 μm to 3 μm and a long axis of about 5 μm to 20 μm. Was. Incidentally, the particle morphology is a common particulate form to _{Na 2 Ti 3 O 7, K} 2 Ti 4 O 9 and _Cs 2 _Ti 5 _{O 11} of the monoclinic phase.

Next, with respect to this precursor (900 ° C. calcined sample), the hydrochloric acid solution is exchanged every 12 hours for 5 days using hydrochloric acid in accordance with the production method disclosed in Patent Document 3 described above, and the ion exchange reaction. And titanic acid was obtained.
The obtained titanate was heat treated for 4 hours at 450 ° C., to obtain a titanium dioxide bronze phase _(TiO 2 (B)).

When this titanium dioxide (TiO ₂ (B)) was analyzed by the X-ray diffraction (XRD) method, the X-ray diffraction (XRD) diagram was similar to the X-ray diffraction (XRD) diagram of Comparative Example 1.
The measured Raman spectrum in the titanium dioxide (TiO 2 _(B)), consistent with the Raman spectrum of Example 1.

Next, an electrode was prepared using the titanium dioxide (TiO ₂ (B)) as an active material. In preparing the electrode, 15 mg of a conductive binder composed of acetylene black and Teflon (registered trademark) was used, and the active material was 25 mg.
Further, the electrolyte, 1M LiPF ₆ (lithium hexafluorophosphate) / ethylene carbonate (EC) - was used dimethyl carbonate (DMC).
And the electrode which used the titanium dioxide which concerns on this comparative example 2 for an active material, and a metal lithium counter electrode are combined, and a lithium secondary battery is comprised with electrolyte solution.

The charge / discharge curve of the lithium secondary battery (Comparative Example 2) provided with the electrode and the electrolyte has a typical titanium dioxide (TiO ₂ (B)) shape, and its differential curve (dQ / dV) is It had only one peak below 2V.

  As described above, the titanium dioxide according to the present embodiment can provide a lithium ion secondary battery exhibiting excellent initial discharge capacity and initial charge / discharge efficiency when used as an electrode material of a lithium ion secondary battery. There is an effect of being able to. In addition, when titanium dioxide according to this embodiment is used as an electrode material for a lithium ion secondary battery, the diffusion distance of lithium ions in the crystal is short, and the titanium dioxide is synthesized by heat treatment at high temperature. Therefore, the irreversible capacity accompanying the decomposition of the electrolytic solution is reduced.

In the present embodiment, the case where titanium dioxide is used as the negative electrode active material of the lithium ion secondary battery has been described. However, titanium dioxide may be used as the negative electrode active material of the hybrid capacitor.
Here, the hybrid capacitor is one in which an electric double layer is used for one of two electrodes and a redox reaction (redox reaction) is used for the other electrode.
In particular, as an example of a hybrid capacitor, there is a lithium ion capacitor that uses an electric double layer for a positive electrode and a lithium ion secondary battery for a negative electrode.
That is, by combining a negative electrode composed of a lithium ion secondary battery using titanium dioxide according to the present embodiment as a negative electrode active material and a positive electrode of a carbon material such as activated carbon, it is applied to a hybrid capacitor (lithium ion capacitor). Can do.
In addition, since the potential of the negative electrode using the lithium ion secondary battery according to the present embodiment is about 1.6 V, a hybrid capacitor (lithium ion capacitor) with an active carbon having an average voltage of 1.4 V as a positive electrode or an average A hybrid capacitor having graphite as a positive electrode with a voltage of 2.5 V or more can be produced.

Claims (6)

Titanium dioxide is a microcrystalline aggregate as an aggregate of primary particles generated from titanium oxide containing an alkali metal,
The primary particles are spherical particles having a layered structure and having a particle diameter of 1 μm or less,
The titanium dioxide is characterized in that the microcrystalline aggregate has no orientation. In the titanium dioxide according to claim 1,
Titanium dioxide, wherein the primary particles are produced by firing the titanium oxide at 500 ° C to 800 ° C. In the titanium dioxide according to claim 1 or 2,
Titanium dioxide peak of 367cm ^-1 in the Raman spectrum, characterized in that appears as a shoulder peak of the 410cm ^-1 in the Raman spectrum.   A lithium ion secondary battery comprising the titanium dioxide according to any one of claims 1 to 3 as a negative electrode active material.   A hybrid capacitor comprising the lithium ion secondary battery according to claim 4 as a negative electrode. A baking step of baking an alkali metal-containing titanium oxide at 500 ° C. to 800 ° C .;
A titanic acid production step of impregnating the calcined titanium oxide in an acidic aqueous solution to produce titanic acid;
A titanium dioxide production step of firing the produced titanic acid to produce titanium dioxide;
The manufacturing method of the titanium dioxide characterized by including.